The invention relates to a liquid crystal display device comprising a liquid crystal display cell having a layer of nematic liquid crystal material which is present between two substrates provided with electrodes, and at least a polarizer and at least an optically anisotropic layer. The invention also relates to a retardation foil or retardation layer for use in, for example liquid crystal display devices.
Such display devices are generally used in, for example monitors, TV applications and, for example display devices in motorcars and aircraft, and for instruments. The foils (and retardation layers) may also be used in angle-invariant optical delay devices.
A display device of the type described in the opening paragraph is known from EP-A-0 423 881 (PHN 13.108). In this Application, a compensation foil comprising an optically anisotropic layer of a polymer material with a cholesteric ordering is used to inhibit discoloration in a twisted-nematic display device and obtain a high contrast. The polymer material is ordered in such a way that a molecular helix can be distinguished, with the axis of the helix being directed transversely to the layer.
However, display devices in which such compensation foils are used still have a large angle dependence, i.e. the contrast is very much dependent on the angle at which and the direction from which the display device is being watched, unless the pitch of the helix of the polymer material is chosen to be very small. Manufacture of such polymers having a cholesteric helix with a small pitch requires very cumbersome process steps, because one stereo isomer must be isolated every time so as to obtain the desired molecular rotation, while, moreover, the materials suitable for this purpose are very expensive.